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Deposit Synonyms
Roxby Downs; Sml 1
Mineral District
Deposit Summary
IOCGU deposit in host breccia complex, with significant contained iron, dominantly as hematite, and not currently considered to be economically recoverable. Resource 2018 10,727Mt @ 0.72%Cu, 230g/tU3O8, 1.28g/tAg, 0.30g/tAu.
Deposit Description
OLYMPIC DAM, world's largest known uranium deposit and one of the largest known copper deposits, also with economic gold, silver, and with significant but uneconomically recoverable iron and REE (particularly lanthanum and cerium). Also elevated barium, and fluorine. Total resource (June 2022), 11,320Mt @ 0.71%Cu, 0.023% U3O8, 1.31 g/t Ag, and 0.31 g/t Au. Estimated production from 1988-2017 from ~190Mt ore treated at initial resource grades of 2.36%Cu, 0.54g/tAu, 5.4g/tAg, 676ppmU for actual recovery of 3.94Mt copper cathode product, >2Moz refined gold, >17.8Moz refined silver, and > 84,000 tonne U3O8 concentrate.
Host to mineralisation is the Roxby Downs Granite, and within a zone of iron enrichment that includes the Olympic Dam Breccia Complex. This is a hydrothermal breccia system, with an overall H-shape, with an elongate linear NE arm. Economic mineralisation persists for ~10 km NS to ~4 km wide. Cover is ~350m of flat-lying metasediment of the Pandurra Formation, in turn unconformably overlain by Neoproterozoic metasediment, in turn overlain by younger sediment of the Eromanga Basin.
The mineralised breccia complex demonstrates a deposit scale mineralogical zonation of progressive increase in Fe to a central core of massive hematite breccia, zonation of sulphides from outer pyrite => chalcopyrite => bornite => chalcocite, uraninite => coffinite => brannerite. The bornite-chalcopyrite boundary is well defined and highly convoluted. There are 3 styles of gold mineralisation including gold as accessory mineral in Cu-U ore, and in separate, higher grade Au-only zones. Estimated average light REE is >3,000ppm, and heavy REE plus yttrium at >100ppm. REE mineralogy dominantly bastnasite and florencite.
The southern sector south of the Jubilee Fault shows a lithological zoning of outer hematite-qz breccia => volcanic breccia => interbedded mudstone-sandstone => interbedded green sandstone-mudstone. The richer ore may occur as discrete zones. Within these zones the more hematite-rich breccias are the most strongly mineralised as disseminated copper sulfides, and uranium ore. Significant
Metal precipitation was thought to have proceeded by coupled redox reactions resulting from the mixing of ascending hot, reduced, Fe-rich waters with cooler meteoric and/or lacustrine waters occupying near-surface parts of the breccia complex. The ore environment was interpreted as a major breccia complex formed by the interplay of hydrothermal, volcanogenic, sedimentary and tectonic processes.
Recent academic studies suggest OD is a dismembered ore deposit, with a geological history of initial ore deposition in an intense, hydrothermal breccia system dated from ~1595-1590Ma. The deposit has subsequently been modified in its form, and ore mineralogy by later orogenic events, in particular a major sinistral wrench structure at 1200-1050 Ma (Morrissey et al), and episodic fluid remobilisation events corresponding to orogenic events. In particular significant uranium input during the Delamerian (515-485Ma).
On site processing of ore for products of copper cathode metal, gold and silver bullion. Iron ore (~24%Fe) and REE grades (0.5% TREE, Oreskes & Einaudi, 1990), are considered too low or too metallurgically difficult to recover economically. Rare earth oxides at Olympic Dam finish up in the tailings storage facility at the mine site.
Discovery Year
? 1975
Commodities
Copper, Gold, Silver, Iron, Rare Earths, Uranium Oxide, Uranium
Ore Minerals
Argentite, Bornite, Brannerite, Chalcocite, Chalcopyrite, Coffinite, Copper, Digenite, Djurleite, Florencite, Gold, Molybdenite, Silver, Sphalerite, Synchysite, Uraninite, Uranium Minerals (Non Specific)
Gangue Minerals
Barite, Bastnaesite, Chlorite, Feldspar, Fluorite, Hematite, Hematite Micaceous, Monazite, Pyrite, Quartz, Rare Earths, Sericite, Siderite, Xenotime
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